Using measurements on signals of terrestrial transmitters for positioning purposes may be of particular interest at indoor locations, where satellite signals for a satellite signal based positioning may not be available or not be available with sufficient signal strength.
The terrestrial transmitters may belong for instance to access points of wireless local area networks (WLAN), to Bluetooth® (BT) devices or to Bluetooth low energy (BLE) beacons. Such transmitters broadcast standard signals in order to advertise their presence. In some cases, they may advertise in this way availability to mobile devices seeking a connection. The signals may convey information in the form of packets of predefined format, and the information may include at least an identifier of the transmitter. The transmitters may be visible to any mobile device with suitable radio interface, regardless of whether or not they are known to the mobile device. The broadcast signals are equally referred to as beacons.
A terrestrial transmitter based positioning at a particular site may be based on radio maps, which allow determining for instance which received signal strengths of which transmitters can be expected at various locations of the particular site.
For making use of a positioning service, a mobile client device may detect signals broadcast by a plurality of transmitters and measure their signal strengths. The mobile device may send results of the measurements along with identifiers of the transmitters to a positioning server. An identifier may be for instance in the form of a service set identifier (SSID) and the results of measurements may be for instance in the form of a received signal strength indicator (RSSI). The positioning server may evaluate the signals taking account of data stored in radio maps and return coordinates that are consistent with the measured signal strengths of the plurality of transmitters.